1. Field of the Invention
This invention relates to a sheet cutting apparatus for cutting a stack of sheets. This invention particularly relates to a sheet cutting apparatus for cutting a stack of large-sized sheets into a plurality of small-sized stacks of sheets.
2. Description of the Prior Art
When a stack of large-sized sheets is to be cut into a plurality of small-sized stack of sheets, the stack of large-sized sheets has heretofore been inclined and vibrated so that the edges of the stacked large-sized sheets are aligned. The stack of large-sized sheets, the edges of which have thus been aligned, is then pushed by a press roll from above, and air is thereby removed from between the sheets. Thereafter, the stack of sheets is subjected to a trimming process, a process for cutting into medium-sized sheets, and a process for cutting into small-sized sheets, which processes are carried out in this order by an ordinary plain cutting machine.
The process for removing one stack of sheets from a plurality of stacks of sheets, the process for feeding a stack of sheets into a sheet cutting machine, and the process for piling up a plurality of stacks of cut sheets are typically automated. Also, various techniques have been proposed to facilitate the sheet cutting work. A technique for changing the direction of a stack of sheets on a sheet cutting machine is proposed in, for example, Japanese Unexamined Patent Publication No. 61(1986)-295947. Also, a technique for aligning the edges of stacked sheets on a sheet cutting machine in proposed in, for example, Japanese Unexamined Utility Model Publication No. 58(1983)-4397. Additionally, techniques for taking the stacks of cut sheets out of a sheet cutting machine are proposed in, for example, Japanese Unexamined Patent Publication 55(1980)-89146 and Japanese Unexamined Utility Model Publication No. 55(1980)-142293.
In order to increase the efficiency with which a series of processes for cutting stacks of sheets are carried out, and to decrease the working force required for such processes, it is desirable that all of the operations from the process for feeding stacks of sheets into a sheet cutting machine to the process for feeding the stacks of cut sheets out of the sheet cutting machine be automated. Heretofore, as described above, improvements have been carried out on each individual process, and the process for feeding a stack of sheets into a sheet cutting machine has been performed automatically. However, operations of the sheet cutting machine for cutting a stack of sheets have heretofore been carried out manually.
One of the reasons why the sheet cutting operations, which are the main operations in the sheet cutting machine, have heretofore been carried out manually is that some of the stacked sheets, and in particular, the sheets at the upper part of the stack of sheets, shift in position when the stack of sheet is cut, when the direction of the stack of sheets is changed on the sheet cutting machine, or when the stack of sheets is conveyed on the sheet cutting machine. As a result, problems often occur that the sheets when have been cut and are located adjacent to each other overlap each other. Therefore, it is necessary for an operator to monitor whether or not such an overlap of sheets occurs.
In general, a sheet cutting machine is constructed such that when a stack of sheets is cut, a cutting blade is pulled in the direction along which the stack of the sheets is to be cut while the cutting blade is moved downwardly. Therefore, when the stack of sheets is cut, some of the stacked sheets, and in particular, the sheets at the upper part of the stack of sheets, readily shift in position in the direction in which the cutting blade moves. If some of the stacked sheets thus shift in position, the sheets when have been cut and are located adjacent to each other easily overlap each other, and adverse effects occur on the cutting operations. For example, a stack of large-sized sheets is cut into a plurality of stacks of medium sized, long strip-like sheets. While the stacks of the medium-sized, long strip-like sheets are placed side by side with one another, they are simultaneously cut into a plurality of stacks of small-sized sheets in a direction which is normal to the direction along which the stack of large-sized sheets was cut into the stacks of the medium-sized sheets. In such cases, if the medium-size sheets overlap each other, the sheets cannot be cut accurately.
In cases where scratching of the surfaces of the sheets is allowable, the sheets can be prevented from shifting in position by removing air from the sheet stacks and causing the sheets of each sheet stack to closely contact one another by use of a press roll. However, in cases where the surfaces of the sheets easily undergo scratching or should be prevented from being scratched, strong pressing of the sheets by a press roll must be avoided. Therefore, in such cases, air cannot be sufficiently removed from the stack of sheets, and the sheets will easily shift in position. Accordingly, during the sheet cutting operation, it is necessary for the operator to monitor whether or not the sheets shift in position.